1. Field of the Invention
The present invention relates to a mask for the manufacture of semiconductor devices such as semiconductor elements, liquid crystal display elements, image pick-up devices (CCDs etc.), or thin film magnetic heads and the like, and to an exposure method and a method of manufacturing semiconductor devices.
2. Background Art
In the photolithography process for manufacturing semiconductor devices, a circuit pattern is printed onto a photosensitive substrate, and various processes such as development and etching are performed on the substrate. The circuit pattern is formed on an original plate such as a photomask or reticle, and in general, the image thereof is transferred to a resist layer on the photosensitive substrate via an optical system of an exposure apparatus. With the yearly advancement in high integration of semiconductor devices, in the photolithography process, in order to manufacture even higher quality devices, inspection is made of the process conditions and the apparatus characteristics.
In this inspection, there is the case where the dimensions of the pattern actually formed on the process substrate (the line width etc.) are measured, and the optical characteristics of the exposure apparatus and the process conditions are verified. As a technique for measuring the dimensions of the pattern, heretofore the methods which are generally adopted are; a method of observing the pattern image with an ITV camera via an optical microscope, a method of obtaining the pattern edge of the image using a laser spot light, and a so called SEM method which uses intensity of secondary electrons generated by an electron beam.
However, with abovementioned methods, in order to measure the pattern dimensions, there are the following problems. At first, with the method using an ITV camera and the method using a laser spot light, since there is a light diffraction phenomena, then for example if only the width of one line pattern image is simply detected, there is naturally a limit to the resolution. In particular, with the laser spot method, since the spot size does not fall below the diffraction limit, measurement is not possible for line widths below the spot size. Furthermore, in the method using an ITV camera, although operation is simple, the characteristics of the object lens of the microscope for enlarged viewing of the pattern image, influence the direct resolution or measurement accuracy. On the other hand, in the SEM method, in order to measure the lens image after placing the wafer as a sample into a high vacuum chamber, the operation for preparing the measurement conditions such as the exhaust operation takes time, so that there is a reduction in measurement throughput.
Therefore, the present applicant, in U.S. Pat. No. 4,908,656 (corresponding to Japanese Unexamined Patent Application, First Publication No. Hei 2-31142), has proposed a method for measuring the pattern dimensions by doubly exposing the photosensitive substrate with a substantially linear inspection pattern (a dark part or a light part on the mask or reticle) so as to intersect at a predetermined intersection angle, and using the image such as a wedge-shaped image formed on the substrate. According to this technique, by forming the doubly exposed image, then compared to the case where an image which has been formed by only one exposure is directly measured, it is possible to simply measure the dimensions of the pattern with good reproduction and to a high accuracy. Furthermore, with this technique, also by using the ITV camera or the lens spotlight etc., the pattern dimensions can be measured to a high accuracy.
However, with this technique, at the time of measuring the pattern dimensions, a mask (reticle) having an inspection pattern exclusively for inspection is used. Therefore at the time of actually manufacturing the semiconductor device, it is necessary to change from the inspection mask to a mask having a circuit pattern for actual device manufacture. In the mask exchange operation, there are many operations requiring a comparatively long time such as, examining the front and rear surface of the new mask for foreign objects, and accurately positioning and mounting this mask on the mask stage. Therefore, there is the problem that a large amount of time is required from inspection until shifting to actual device exposure.